Reversing the nutrient drain through urban insect farming-opportunities and challenges

Cities consume the majority of proteins produced globally but have unsustainable, linear food systems from production to consumption to disposal, resulting in significant nutrient losses. The industrial rearing of insects is a promising strategy for converting otherwise lost nutrients back into protein-rich animal feed and fertilizer, particularly to supplement local food production. The black soldier fly (BSF), Hermetia illucens, has been identified as a candidate for industrial rearing. BSF has a superior feed conversion ratio and cycle-time compared to other edible insects and can convert and recover nutrients from a vast variety of organic materials to protein, oil and chitin making it an attractive solution for the management of urban organic solid waste. With an increasing awareness of the environmental urgency and interest in the economic potential of the technology, this review discusses the technological factors confounding the upscaling of insect farming in urban and peri-urban contexts using BSF as a case study. These include the challenges of feed homogenisation and pre-treatment, of integrating insect life-cycle factors (e.g. mating) with bioprocess engineering concepts (which complicates automation), of meeting the nutritional requirements of the larvae at different stages of growth in order to maximize bioconversion and product quality, and of elucidating the impact of microbiome on complex behaviours and bioconversion. A multidisciplinary effort is therefore required to lead urban insect farming to full development to ultimately contribute to future food security.